What could have caused a pumpkin pie to turn green when it was baked?

It's very unlikely that a pumpkin pie would turn green while baking. Here's why:

* Pumpkin color: Pumpkin puree is naturally orange. Even if it's a bit off-color, it won't turn green in the oven.

* Ingredients: The other ingredients in a pumpkin pie (sugar, spices, eggs, milk/cream) wouldn't contribute to a green hue.

* Chemical reactions: There's no known chemical reaction in baking that would cause a pie to turn green.

Possible Explanations for a Greenish Appearance:

* Mold: If the pie was stored improperly and mold developed, it could appear greenish.

* Lighting: The lighting in your kitchen could make the pie appear greener than it actually is.

* Over-mixing: Over-mixing the batter can lead to a denser, more compact texture, which could make the pie appear more green.

* Wrong type of pumpkin: While unlikely, using a variety of pumpkin that's not meant for pies could affect the color.

If you're concerned, it's best to err on the side of caution and not eat the pie.